Brooke,
I had the very same encounter in 1989/1990.
I received the new 3458A in November 1989, and only 1 month later, on 1st January 1990, the New Volt (SI-1990) went effective.
As my instrument came directly from the U.S., the difference in calibration was 9.264ppm, which the instrument now was reading high.
You may read my whole volt-nuts story related to this SI - change here:
http://www.eevblog.com/forum/metrology/1000-my-(hi)story-of-the-weston-cell-of-the-volt-and-of-being-a-volt-nuts/.
The 332B might not have been your reference standard, as its uncertainty is 10ppm / 60days only.
Maybe you had a 732A, or a bank of Weston cells in your lab, otherwise this change could not securely be observed by a solitary Fluke 33xB/D.
best regards
Frank
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